Tony Seba is a lecturer in entrepreneurship and clean energy at Stanford University. He is the author of “Solar Trillions – 7 Market and Investment Opportunities in the Emerging Clean-Energy Economy” and “Winner Takes All – 9 Fundamental Rules of High Tech Strategy“.
Mr. Seba is a Silicon Valley serial entrepreneur having founded or co-founded several cleantech and high-tech companies.
He is a keynote speaker at clean energy, cleantech, entrepreneurship and high-tech conferences and company events.
Tony Seba holds an M.B.A. from Stanford University Graduate School of Business and a B.S. in Computer Science and Engineering from the Massachusetts Institute of Technology.

The World's First Baseload (24/7) Solar Power Plant

In the future solar power plants will be as plentiful as personal computers or cell phones are today and they will generate energy on demand. Today I have witnessed the future of energy: a solar power plant capable of generating solar electricity around the clock.

Located in the Spanish province of Andalucia, Torresol Energy’s Gemasolar is the world’s first utility-scale commercial baseload solar power plant.

Gemasolar - The World's First Baseload (24/7) Solar Power Plant

Torresol Energy, the company that built Gemasolar is a joint venture between Spanish infrastructure giant Sener and Masdar – Abu Dhabi’s Future Energy Company. During my visit to Gemasolar I met with Santiago Arias, Torresol’s Chief Infrastructure Officer and one of the co-founders of the company.

Solar Salt Batteries

Gemasolar, which officially launched last month (May 2011), is a 19.9-MW plant with a 15-hour ‘battery’. Gemasolar’s expected production is 110,000 MWh per year—or about enough to fully power 25,000 households. Because it can store energy, this 19.9 MW generates the equivalent of a 50 MW solar power plant without storage, according to Mr. Arias.

Gemasolar’s battery consists of two tanks of molten salt thermal energy storage that allows the solar plant to generate on-demand electricity: during the evening, during cloud cover or rain, or even days or weeks later. Molten salt energy storage (MSES) or ‘solar salt’ batteries are thermal not chemistry-based batteries like Lithium-ion which power electric vehicles like Tesla’s (Nasdaq: TSLA) Roadsters.

MSES uses a combination 60% potassium nitrate and 40% sodium nitrate which retains 99% of the heat for up to 24 hours. Another way to put this number: this battery loses just 1% of the heat energy per day.(1)

Potassium nitrate happens to be environmentally safer and cheaper than most chemical-based battery alternatives. In the Middle Ages, this ingredient was used to preserve food and it is still used in the production of corned beef.(2) Potassium nitrate is also used in toothpaste (for sensitive teeth) as well as in garden fertilizers. MSES capital costs are also relatively low, clocking in at $50 to $100 per kWh, compared to about ten times that for a Li-on battery that powers a personal computer or electric vehicle.

Gemasolar is not the world’s first commercial solar plant with MSES. If I had driven another 300 Km (186 miles) due south-east on Andalucia’s A94 highway I would have seen Andasol-1, a 50 MW CSP plant that has been operating with a 7.5-hour battery since July 2009. Gemasolar basically doubled the battery availability to 15 hours.

Torresol’s Arias expects Gemasolar to produce electricity about 6,400 hours per year - a capacity factor of 75%. For comparison, the Hoover Dam has a capacity factor of just about 23% while China’s Three Gorges hydro-electric power plant has a capacity factor of about 50%.(3) According to a 2003 study by Clemson University Prof Michael Maloney in 2003 the capacity factor of nuclear reactors in Japan, France, and the US were in the 65% to 72% range and the worldwide load factor was 69.4 percent.(4)

Solar Power Tower

When most people think about solar power, they think of photovoltaic (PV) panels on the roof of a house or building. PV converts photons directly into electricity. Gemasolar belongs to a category called Concentrating Solar Power (CSP) which use the sun’s energy to heat a fluid (water, synthetic oil or molten salt) to generate steam which then drives a turbine to generate electricity.

If you’ve ever used a magnifying glass or better yet a concave mirror to focus sunlight and burn a hole in a piece of paper, you get the idea. Use thousands (or millions) of square meters of mirrors (not PV panels) to reflect that same sunlight on a single point (actually small area), and you can heat a fluid flowing past it up to several hundred degrees Celsius and use that superheated fluid to drive an industrial-scale turbine.

Each heliostat has reflective mirror surface about 110 square meters (1,184 square feet) and follows the sun using two motors with built-in pogrammable logic controllers (PLC) that recalculate and readjust the heliostat’s position 15 times per minute. As I walked under the heliostats I could hear the slight hissing sound of the motors moving the heliostats every 4 seconds. I went up to a heliostat to touch the reflective surface mirror and sure enough it was a mirror, not metal. When I asked Mr Arias about it, he said that these are slightly better mirrors than what I would have in my house.

Energy Storage changes everything

Santiago Arias, Torresol’s Chief Infrastructure Officer, started building power plants 38 years ago. He converses about the electricity market and gets excited about the impact of a solar power plant that can operate around the clock. “The maximum demand for electricity takes place during the evening on the hottest days of the year,” says Mr Arias. The market pays a premium price for electricity during those peak hours. A solar power plant generates the most energy precisely during those hot sunny days.

“The ability to store energy when the sun it at its peak and deliver it when the market demand is at its peak changes everything in the power market. My fuel cost is zero. Natural gas can simply not compete with us.”

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While a baseload solar power plant would certainly be interesting, this article presents a very optimistic view of an unbuilt and unproven technology. There are two areas worthy of more detailed analysis from the outset:

1) Capital cost estimates for this MSES are way out of line with what experience in building solar energy systems has been up to this point: the $737 million, 110 MWe plant to be built in Nevada has capital costs of $6700/kWe, which is an order of magnitude higher than what is cited by the author of this article. Conventional estimates for this type of power plant often put capital costs in the neighborhood of $10000/kWe; this $10000/kWe was obtained through conversations with experts in the field prior to the approval of the $737 million plant in Nevada being approved. Keep in mind that this proposed Nevada plant hasn’t been built yet and may experience great cost overruns.

2) The capacity factor estimate of 75% is compared to an operating history over the entire lifetime of nuclear power. This is an unfair comparison: when nuclear power was new, outages were far more frequent. In recent years, the capacity factor for nuclear power plants in the US has exceeded 90% due to excellent plant management practiced developed over the course of the preceding decades. To suggest that a 75% capacity factor will be achieved out of the gate seems optimistic. The capacity factor will ultimately be a function of how well the power plant is managed, what management values, and what technologies and operating practices are created and instituted to meet these objectives. Even among nuclear operators, there is little doubt operating practices differ from country to country; why would this be different for solar?

@energynut: I stand by the reporting in my article. The plant is built. It works. Both these technologies (molten salt energy storage and solar power towers) have been around for decades.

The molten salt energy storage capital costs I quote are correct. You’re confusing the capital costs for the energy storage (which I quote in my article) with the total cost of the whole plant (which includes turbines, the heliostat field, the tower – and the battery) which is what you’re quoting. Check out this Scientific American article for more on molten salt being used at a commercial solar plant in Spain. Please notice that they say the capital cost for MSES is $50/kWh – which is the low-end of the range I use. http://www.scientificamerican.com/article.cfm?id=how-to-use-solar-energy-at-night

It means that if the tank of molten salt is fully heated, it could generate 19.9 MW for 15 hours, i.e. it contains about 300 MW-h of usable energy. The 1% means that the insulated tank cools off at a rate of about 3 MW-h per day if it’s just left sitting. (About 375 kW of heat?)

To answer my own question, the graph in this article http://www.greentechmedia.com/articles/read/solar-all-day-and-night/ suggests the cost is $18/W, or a total of $360 million. They’d probably have done better to double the generating capacity, so they could sell more power during the evening and less in the middle of the night.